The present disclosure relates generally to wireless communication systems, and more particularly, to techniques for contention-based random access in unlicensed spectrum.
Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, and broadcasts. Typical wireless communication systems may employ multiple-access technologies capable of supporting communication with multiple users by sharing available system resources. Examples of such multiple-access technologies include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single-carrier frequency division multiple access (SC-FDMA) systems, and time division synchronous code division multiple access (TD-SCDMA) systems.
These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example telecommunication standard is Long Term Evolution (LTE). LTE is a set of enhancements to the Universal Mobile Telecommunications System (UMTS) mobile standard promulgated by Third Generation Partnership Project (3GPP). LTE is designed to support mobile broadband access through improved spectral efficiency, lowered costs, and improved services using OFDMA on the downlink, SC-FDMA on the uplink, and multiple-input multiple-output (MIMO) antenna technology. However, as the demand for mobile broadband access continues to increase, there exists a need for further improvements in LTE technology. These improvements may also be applicable to other multi-access technologies and the telecommunication standards that employ these technologies.
In LTE, an evolved Node B (eNB) allocates dedicated physical random access channel (PRACH) resources to each user equipment (UE) listening for a transmission from the eNB on a communication channel. Each UE may then use the dedicated PRACH resource to transmit data to the eNB on the communication channel. However, if the eNB does not have any downlink traffic to transmit and/or the eNB is not aware of UEs located in a cell of the eNB, then the eNB may not allocate dedicated PRACH radio resources to the UEs. As a result, each UE may not be able to access the communication channel. Accordingly, techniques that allow for such access by allocating the appropriate resources are desirable.